code: def change_opacity(slider):
      slicer_opacity = slider.value
      image_actor_z.opacity(slicer_opacity)
      image_actor_x.opacity(slicer_opacity)
      image_actor_y.opacity(slicer_opacity)
  
file_path: dipy/doc/examples/viz_advanced.py
imports: import numpy
  from dipy.data.fetcher import fetch_bundles_2_subjects, read_bundles_2_subjects
  from dipy.tracking.streamline import Streamlines
  from dipy.viz import actor, window, ui
label_desc: Use image node_id 4 for calling a global function with example usage: change_opacity(slider) without return types